Arabidopsis annexin1 mediates the radical-activated plasma membrane Ca2+ - and K+ -permeable conductance in root cells

Plant cell growth and stress signaling require Ca2+ influx through plasma membrane transport proteins that are regulated by reactive oxygen species. In root cell growth, adaptation to salinity stress, and stomatal closure, such proteins operate downstream of the plasma membrane NADPH oxidases that produce extracellular superoxide anion, a reactive oxygen species that is readily converted to extracellular hydrogen peroxide and hydroxyl radicals, OH_. In root cells, extracellular OH_ activates a plasma membrane Ca2+-permeable conductance that permits Ca2+ influx. In Arabidopsis thaliana, distribution of this conductance resembles that of annexin1 (ANN1). Annexins are membrane binding proteins that can form Ca2+-permeable conductances in vitro. Here, the Arabidopsis loss-of-function mutant for annexin1 (Atann1) was found to lack the root hair and epidermal OH_-activated Ca2+- and K+-permeable conductance. This manifests in both impaired root cell growth and ability to elevate root cell cytosolic free Ca2+ in response to OH_. An OH_-activated Ca2+ conductance is reconstituted by recombinant ANN1 in planar lipid bilayers. ANN1 therefore presents as a novel Ca2+-permeable transporter providing a molecular link between reactive oxygen species and cytosolic Ca2+ in plants

Effect of supplemental Ca2+ on NaCl-stressed castor plants (Ricinus communis L.)

Greenhouse experiments were conducted to assess the effects of supplemental Ca2+ in salinised soil on germination and plant growth response of castor plant (Ricinus communis L. Var. Avani-31, Euphorbiaceae). NaCl amounting to 390 g was thoroughly mixed with soil of seven lots, of 100 kg each, to give electrical conductivity of 4.1 dS m–1. Further, Ca(NO3)2 × 4H20 to the quantity of 97.5, 195, 292.5, 390, 487.5, and 585 g was separately mixed with soil of six lots to give 1:0.25, 1:0.50, 1:0.75, 1:1, 1:1.25, and 1:1.50 Na+/Ca2+ ratios, respectively. The soil of the seventh lot contained only NaCl and its Na+/Ca2+ ratio was 1:0. Soil without addition of NaCl and Ca (NO3)2 × 4H20 served as control, with a 0:0 Na+/Ca2+ ratio. Salinity significantly retarded seed germination and plant growth, but the deleterious effects of NaCl on seed germination were ameliorated and plant growth was restored with Ca2+ supply at the critical level (1:0.25 Na+/Ca2+ ratio) to salinised soil. Supply of Ca2+ above the critical level further retarded seed germination and plant growth due to the increased soil salinity. Salt stress reduced N, P, K+ and Ca2+ content in plant tissues, but these nutrients were restored by addition of Ca2+ at the critical level to saline soil. In contrast, Na+ content in plant tissues significantly increased in response to salinity, but significantly decreased with increasing Ca2+ supply to saline soil. The results are discussed in terms of the beneficial effects of Ca2+ supply on the plant growth of Ricinus communis grown under saline conditions

Energy costs of salinity tolerance in crop plants

Stephen D. Tyerman, Rana Munns, Wieland Fricke, Borjana Arsova, Bronwyn J. Barkla, Jayakumar Bose, Helen Bramley, Caitlin Byrt, Zhonghua Chen, Timothy D. Colmer, Tracey Cuin, David A. Day, Kylie J. Foster, Matthew Gilliham, Sam W. Henderson, Tomoaki Horie, Colin L.D. Jenkins, Brent N. Kaiser, Maki Katsuhara, Darren Plett, Stanley J. Miklavcic, Stuart J. Roy, Francisco Rubio, Sergey Shabala, Megan Shelden, Kathleen Soole, Nicolas L. Taylor, Mark Tester, Michelle Watt, Stefanie Wege, Lars H. Wegner, and Zhengyu We

Quantitative expression analysis of TaSOS1 and TaSOS4 genes in cultivated and wild wheat plants under salt stress

Salt stress is a mixture of ionic, osmotic, and oxidative stresses. The expression of TaSOS1 (a transmembrane Na(+)/H(+) antiporter) and TaSOS4 [a cytoplasmic pyridoxal (PL) kinase] genes were measured in four different salinity levels and different time courses of salinity exposure using qRT-PCR technique. Mahuti (salt tolerant) and Alamut (salt sensitive) cultivars were used as cultivated wheat, and T. boeticum and Aegilops crassa as wild wheat plants. Salt-induced expression of TaSOS1 in these wild wheat plants indicates the presence of active TaSOS1 gene on the genomes A and D. The TaSOS1 and TaSOS4 transcript levels were found to be downregulated after salt treatment in all cultivars except in A. crassa, which was in contrast with its expression pattern in roots that was being upregulated from a very low-basal expression, after salt treatments. Duncan's Multiple Range Test showed a significant difference between expression in the 200-mM NaCl concentration with the 50 and 100 mM for the TaSOS1 gene, and no significant difference for TaSOS4. Lack of significant correlation between the TaSOS1 and TaSOS4 gene expressions confirms the theory that PLP has no significant effect on the expression of the TaSOS1 gene in wheat leaves.Amin Ramezani, Ali Niazi, Ali Asghar Abolimoghadam, Mahboobeh Zamani Babgohari, Tahereh Deihimi, Mahmod Ebrahimi, Hosein Akhtardanesh, Esmail Ebrahimi